Bundled es6.js for client

[abhijeetkpawar]

It will be good to have bundled es6.js and probably es7.js, so as to include only that part for client usage

[zloirock]

Here 2 problems:

• It's additional size in the package. Someone still uses npm@2, core-js is a too frequent dependency and sometimes we have dozens of core-js copies in node_modules. I have too many issues about core-js package size. It could be solved by creating separate packages with bundles, but...
• the second problem is core-js architecture. It's many small separate modules, they use shared helpers and stores. Usage both - es6 and es7 - separate bundles can cause problems with interaction those modules and will add additional size.

Most likely, in core-js@3 we will have only 1 default bundle - with a global shim. If you wanna something specific - you can bundle it yourself.